Electric circuit equalization



June 29, 1948.

Filed Dec. 7, 1944 K. W. PFLEG ER 3 SheetsSheet 1 FIG.

I -10 3 /4 TRANSDUCER 9 a?) DELAY MEMBER s E F 2 \D [7 //a DELAY MEMBERI /9 l v I 22 ATTENUATOR DE), ("4'' BE IN MEMBER EOUALIZER) 3 F l G. 2

( TRANSDUCER 2Q DELAY MEMBER 2/ 2 DELAY MEMBER ATTE/VUATOR DELAY,

(MAY BE IN MEMBER EQUAL/25R) a TRAMmqcER TRANSDUCER TRANSDUCER -f--CORRESPONDING DELI) MEMBERS IN TRANSDUCER-f MAY HAVE DIFFERENT DELAYSlNl/E N TOR K M. PFLEGER ATTORNEY June 29, 1948. K. w. PFLEGER 2,444,063

' ELECTRIC IQIRCUIIEQUALIZATION Filed Dec. 7, 1944 3 Sheets-Sheet '2FIG. 4

/N VENTOR K w P LEGER ATTORNEY June 29, 1948. I K, w, PFLEGER i2,444,063 v ELECTRIC cmcum EQUALIZATION Filed De. 7, 1944 s Sheets-Sheeta FIG. 6

v RESULTAIVT FIG-8 CHARlGZ'ER/STIC 0F LINE .j y W w TRANSDUC RCHARACTER/SWO FREQUENCY RESULTA/VT OF" TWO LOWER CURVES 9 A AVAQA iAim/WA \AfiV v v u u v u rnsouguc? uvvavron K W PFLEGER ATTORNEYPatented June 29, 1948 2,444,063 ELECTRIC omourr EQUALIZATION Kenneth W.Pfleger, Arlington, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. I, a corporation of New York ApplicationDecember '7, 1944, Serial No. 567,065

9 Claims.

This invention relates to electric circuit arrangements and moreparticularly to the attenuation and envelope delay equalization of wavestransmitted over transmission lines.

It is a primary object of this invention to provide novel means forequalizing the attenuation and envelope delay versus frequencycharacteristics of broad band transmission lines 01' systems.

Due to the fact that in long wire line signal transmitting systems theline is usually not electrically smooth, that is, electrical impedanceirregularities appear at many points along the line, small wiggles inthe attenuation and envelope delay (dc/do, where p is the phaseretardation and w is 21r times the frequency in cycles per second)versus frequency characteristics of the system occur. In one of its moreimportant aspects, the invention relates to the removal or reduction ofthese so-called wiggles.

On a coaxial circuit transmitting a band of from 0.3 to 2.8 megacycles,for example, it is possible that the periodicity of the wiggles will beas low as 0.1 of a megacycle which gives around 25 humps or wiggles in atransmission band 2.5 megacycles Wide. The spacing between humps is notnecessarily constant over the frequency range, nor are their amplitudes.On long circuits ordinary equalization produces a more nearly. flatcharacteristic but may give rise to an increased number of wiggles andit is possible to design rather complicated mop-up equalizers toequalize these wiggles. In accordance with the present invention,however, compensatin wiggles are produced in the attenuation andenvelope delay frequency characteristics by means of delayed signals andthe apparatus required is very much less than that of a mop-up equalizerwhich may require many sharply tuned resonant circuits. When the humpsor wiggles are spaced at regular intervals along the frequency band andwhen they are of fairly uniform amplitudes or of amplitudes which varyin a known manner, the saving in apparatus resulting when the presentinvention is utilized may be very great. The compensating humps orwiggles are produced by combining a pair of properly delayed signals(one delay may be substantially zero if desired) produced in branchcircuits with the delayed signal in the main transmission path and, ifnecessary, by repeating this process any desired number of times.

In a specific form of .the invention, chosen by way of example forillustrative purposes, means are provided for diverting at a selectedpoint in the transmission system a portion of the signal and thisportion is passed through an attenuator and then through twoparallel-connected delay networks to produce two delayed signals whichare combined with the .original signal after it has passed through athird delay network. The phase shifts for any particular frequency ofthe signal band in the two parallel-connected delay net works are madeequal to each other but their phases are respectively of opposite signwith respect to the phase of the signal which is passed through thethird delay network, that is, their phases are respectively +0 and -0with respect to that of the wave at the output of the third delaynetwork. The same is true for all frequencies in the band. By means ofthis arrangement compensating attenuation humps with practically nodelay efie'cts are produced, but if the connections from one of the twoparallel-connected delay networks are reversed, compensating envelopedelay humps can be produced with practically no attenuation effects. Ifit is desired to produce wiggles of uniform periodicity and varyingamplitude, the loss can be varied over the frequency range either bymanual or automatic adjustment. If it is desired to produce wiggles ofnon-uniform periodicity, the delay networks, which in the former caseswere of the :type to produce uniform envelope delay over the frequencyband, can be replaced by delay networks or members which do not producea flat delay. Where the desired correction is not a simple sinusoidalcharacteristic with respect to frequency more than one set of delaymembers can. be used in tandem, each with a different amount of delay.By means of a suflicient number of such devices in tandem superimposedsinusoidal components can be obtained to simulate any loss or delaycharacteristic which i resolvable into a Fourier series.

The invention will be more readily understood by referring to thefollowing description taken in connection, with the accompanyingdrawings forming a part thereof in which:

Fig. 1 is a block diagram of a transmission system employing atransducer in accordance with the invention to reduce regularlyrecurring humps in the envelope delay versus frequency characteristic ofthe system;

Fig. 2 is a block diagram of a transmission system employing atransducer to reduce regularly recurring humps in an attenuation versusfrequency characteristic of the system;

Fig. 3 is a block diagram of a transmission system employing a pluralityof the transducers shown in the systems of Fig. 1 or Fig. 2;

, Figs. 4 and 5 are block diagrams of systems employing transducerswhich are modifications of those shown in Fig. 1; and

Figs. 6 to 9, inclusive, are diagrammatic and and a transducer ll! con--The purpose of the transducer transducer is as shown in line Aof Fig.8and.

comprises a number of wiggles of substantially sinusoidal form and ofsubstantially equal amplitude. The purpose, of the transducer IQ is tointroduce a characteristic such as that shown in line B of Fig. 8, whichwill compensate for these wiggles and produce a substantially flatcharacteristic over the transmitted band. This is accomplished bydiverting a portion of the energy from lines [2 and it through anattenuating pad I 3 and through an attenuator- !9 which has a constantloss over the entire frequency range. The output energy of theattenuator I9 is divided-between a delay member 2| (called delay memberNo. l or D1) and, delay member 22 (called delay member No. 3 or D3) theoutput of the delay members I and 3 being combined and applied to thelines 12 and E3 in whichv is inserted a delay member (called delaymember No. 2 or D2). The delay members can be electrical non-dissipativedelay networks or cable pairs or-radio channels or'they can be any othermeans for producing constant envelope delay regardless of changeinfrequency. As one example, each--member electric waves may be convertedinto sound orsupersonic waves by means or a crystal or other form ofloudspeaker for slower propagation in gases or milduids and may bereconverted thereafter into electric waves by meansof acrystal-or-otherform of microphone; The transmitted frequency band may be shifted tohigher frequenciesbeforeconversionfromelectric into supersonic'waves.and after transmission overthe medium maybe shiftedbacls again in ordertomakeuseof-particular speakers -or microphones or desirable. flatcharacteristics. The resultant current at the output of the del aymemberDi D2 and Da-iscomputedbelow. Assume' unit current emergingfrom-Dz; a network or other member haying constant loss and em velope delay.To this must also lie-added currents from D1 and-D3. Let these currentsbe of small amplitude r and" let their phases be I respectively +0-and 0with respect to -the phase ofunittcurrent from D2. This conditionisobtained by making the losses of-DrandDx equal-and bymaking the totaldelay ofthe-pad' I8; attenuator I9 and thenetworkDrlessthan the-delayofDzby the same amount, 'I, asthe total delay ofthepad, attenuator andnetwork D3 is greater than-the delay of D2. The combined output is:

l-|-re+ "re (1) where the minus sign ofthe. latter term is due to areversal of the wires atthe outputof Dc. Equation 1 may be reduced .to:

l+i2r-sin 0 (2) 4 The phase retardation of the resultant, as com-' paredto unit undistorted current is fii== tan 2?" sin 0=2r sin 0 when 21 issmall. I

The envelope delay distortion, that is, the departure from flatness, is

d0 2r Tcosl? (4) where r is the ratio of the current amplitude at theoutput of D1 or D3 to the amplitude at the output of D2 at a frequencyof i 21r and 0 is the phase. difi'erence between currents at the outputsof D1 and D2 or D2 and D3 at such frequency.

Since the desired Wiggles have maxima occurring at uniform frequency ofF cycles over the frequency range of interest asshown in. Fig 8, line A,it is obvious from Equatione that this condition is realized when isconstant and 0 varies as a straight line function of frequencyincreasing by 2 radians every time the frequency varies an amount F sothat in 1 dc: F

Accordingly the wiggles expressed by Equation 4 have the amplitude ru'r27'dw F (5) and therefore T=%TF If the three delaying transducers D1,D2 and D3 have equal losses, then-r denotes the current ratiocorresponding to the loss in the pad Hi; For example, if the delay humpsare twomicro-seconds in-amplitude and-26,-460 cycles apart,

which corresponds to a 31.6-decibel pad.

Since envelope delay is defined as'the derivative of the phase shiftversus 1 characteristic, the phase shift may be determined from thedelay by integration. Thus the phase shifts corresponding to D2 andDsarerespectively.

where M and'm are-constantsofintegration. In order toconserve-apparatus, let the delay member Diand'its phaseshift be zero.-In order to fulfill the requirement given abovethat' the phases ofcurrent D1 andDa" shall be +0and 0'with respect to the ph-ase ofcurrentin the member D2,

+0=wD2+k2=wD3+M-(wD2+)\2)- (8) therefore i 26=wD3+A3=2wD2I-2k2 (9) andLet Equation 8 be differentiated withrespect to w. Then d0 1 1 d =D=37.75 10* 'seconds (11) Similarly from Equation: 9':

D :-%=-7 5:5 X10? secondse (l2) "an iaoce Delay members-are known whichproduce envelope delays of these magnitudes.

It is stated above that the required. phase shiftsare oDz-l-Az and2wD2+2Aa A2 controls the location of the humps as may be seen whenEquation 8 is substituted in Equation 4 giving:

"Accordingly, A2 may be any constant between 0 and Zr depending upon thelocation of F1. When the envelope delay has a minimum at F1 it isevident from Equation 13 thatAat this frequency Suppose, for example,that Dz=37.75 10- seconds and F1=300,000 cycles, then:

A2=21r(N300,000 X 37.75 X 10- A 21r(N 11.325) (16) In order that A2shall be small it may be desirable to select N:1l so that:

'When A2 is other than 0 or 180 it becomes necessary to add a constantphase shift at all frequencies to that of the flat delay medium. Perhapsthe simplest way to obtain the desired over-all phase characteristic isto make the path in the delay medium slightl shorter than would berequired and then add an electrical network or just a few sections oflattice or bridged-T type phaseequalizers in order to make up thedifference plus A2. Methods for designing the latter networks arealready well known to those skilled in the art of equalizer design andneed not be covered here. Thus it is seen that the apparatus required toproduce the delay wiggles of line B l of Fig. 8 consists of a pad laplus two constant delay paths D2 and D3 and a few lattice type networksor their equivalent to obtain the desired values for A2 and As.

The amplitude of the resultant current is /l+lr sin @=1+2 sin 0 when ris small.

Since loge(1+21 :21' when 21 1:; small, it follows that the resultantcurrent has amplitude wiggles corresponding to 2r =2(.02646) =.00l4neper or .012 db. (19) A shown in line B of Fig. 8 can be made to varyover the frequency range rather than all of them being constant as shownin line B of this figure. Thus only four wide band transducers D1, D2,D3 and the attenuator I9 can be made to introduce many delay wiggleswith amplitude and periodicity varying by suitable amountsover thefrequency range with negligible attenuation eifects.

Fig. 6 shows vectorially the relation of the voltages V20 (the outputofthe delay member 20), the voltage V22 (the voltage of the output ofthe delay member 22) and the voltage V21 (the volt- A 15 'tia-lly nophase change.

6 age ofthe output of the delay member-2i This diagram representsvectorially Equation l and it can easily be seen that the resultantvoltage Va "for any particular frequency substantially 5 equal tothe'voltage V20.

"Thesystem shown in Fig. 2 is like that in Fig. l except that theconnections from the output ofdelay member No. 1 are reversedwithrespect to these output connections in the arrangement loshown in Fig.'1. The relations of the voltages V20, Vzr-and V22 in the transducer l Iof Fig, 2 are as= shown in Fig.7. This diagram shows clearly that theresultant voltage Va for any particular frequency has an amplitudechange but substan- The output current at .the terminal l6, I1 is: A

Theredsino delay. effect inthis case. and only..attenuation-humps:result. Therefore this arrangement can pe usedaswanover-all attenuation equalizer withnodelay effects. If the atten-Auation equalizer i9contained within one or'the A other of thearrangements of Figs 1 and 2 does 1 not have constant delay, theover-all output has 5 cy, more than one device may be used in tandemeach with a different value for T. Fig. 3 shows three such devices intandem each transducer being like that shown in Fig. l orAFig. 2.:Bymeans of a suificient number of devices in .w'tandem, superimposed Asinusoidal components, such as are shown graphically in Fig. 9 (wherethe upper curve is the resultant of the two lower curves which are sinewaves of difierentfrequem cies), may be obtained to simulate any loss ordelay characteristic-which is resolvable into a Fourier series; It isobvious that where the char- A acteristic is quite irregular the methodof utilizing delayed signals may be more expensive than I otherzmeans.on account orthe number of delay members in tandem,

"When a large number of transducers It or II are connected in tandem,the amountof apparatus-in the delay networks or other delay members maybecome excessive. Figs. 4 and5 disclose A arrangements wherein some ofthe delay members do multiple duty, thus saving aconsiderable quantityof delay networks.

' Im-ithearrangement of Fig. 4 the transducer A tlldncludes three pathsD1, D2 and D3 .as before 69 but each of these paths includes three delaymembers. The upper path Dz includes the three delay members 50 (having adelay d21),- 5| (having a delaydzz), and 52 (having a delay (22:). "Themiddle path D1 includes the delay members '65 53 (delay (211x54 (delayc112), and55 (delay (in) while the lower path D3 includes the delaymembersEE (delay'-d31);5l (delay (Z32), and 58 (delay dss). Signals fromthe lines l2, I3 are applied 'to the delay memberfill and the outputthereof 70 is applied to the delay member 5! and also, by means'of lines59 and to an attenuating pad Bl the output of which isapplied through anattenuator $2 to conductors B3 and--64 which are connected to theginputterminals of the delay 76" member-54in the path Brand totheinputtermin-als of the delay member 51 in the path D3. The outputterminals of the delay member 5| are connected to the input terminals ofthe member 52 and by means of lines 65 and 66 to an attenuating pad 61the output of which is applied through attenuator 68 to the lines 59 andi which are connected to the input terminals of the delay member 55 inthe path D1 and to the input terminals of the member 58 in the path D3.The signals from the lines 12 and Hi are also applied throughattenuating pad 18 and attenuator I9 to the input terminals of both themembers 53 and 56, the output terminals of which are connectedrespectively to the input terminals of the delay members 54 and 51. Inturn, the output terminals of the members 54 and 51 respectively areconnected to the input terminals of the members 55 and 58. The outputterminals of the delay members 55 and 53 are connected to the outputterminals I6, I! of the transducer 30' to'which output terminals arealso applied the output signals from the delay member 52 in the path D2.By way of example, each of the members 50, and 52 may have a delay (d21,dzz or 1123) of 30 microseconds, each member 53, 54 and 55 may have adelay (du, dlz or (ha) of 15 microseconds while each of the members 56,51 and 58 may have a delay (0131, (132 or 133) equal to .45microseconds. (In other examples, each delay member in a path need notequal the other delay members in the path.) Then Delay D2=d21+d22+d23=9Omicroseconds, Delay D1=d11+d12+d1a=45 microseconds, and DelayD3=d31+d32+d33=135 microseconds.

With this arrangement delayed signals from 45 microseconds to 135microseconds in 15-microsecond steps can be obtained and these are allapplied to the output terminals l6, II. To obtain a delay of 45microseconds the signal travels through the delay members (111, 112 and0313. To obtain a delay of 60 microseconds the signal travels throughthe delay members 0121, 1112 and 213.

' The 75-microsecond delay is obtained by the signal passing through thedelay members (in, dzz and 1113 in tandem. A 90-microsecond delay isobtained by the signal passing through the delay members 1221, 122 anddzs. A delayed signal I05 microseconds behind the input signal isobtained by the signal passing through delay members r121, (Z22 and(133. A 120-microsecond delay is produced by the signal traversing inturn the delay members 0121, (Z32 and (Z33. The l35-microsecond delay isproduced by the signal passing in turn through the delay members (Z31,(132 and dis. All of these figures neglect the delays of the pads andattenuation equalizers which are small compared with the delays producedby the delay memhere, It will be seen that if 90 microseconds isconsidered to be the mean delay, these delay times can be arranged inthree groups, viz., '75, 90 and 105; 45, 90 and 135; and 120, 90 and 60.In each group the difference between the smaller delay and the meandelay is equal to the difference between the mean delay and the largerdelay. Thus three sets of wiggles are produced to compensatecorresponding wiggles in the input signal characteristic, The delaymembers may be nondissipative networks or cable pairs or radio channelsor acoustic members or any other suitable means. The delay in the pathD1 can be zero, if desired, It should be understood that power flows inFig. 4 only in the directions shown by the arrows and that one-waydevices (not shown) such as hybrid coils or amplifiers are provided toprevent power flow in directions contrary to the arrows.

An alternative arrangement to that of Fig. 4 is shown in Fig. 5. In thearrangement of Fig. 5 the path D2 of the transducer 40 comprises asingle large delay member I!) and the path D1 comprises the threesmaller delay members H, i2 and "it (they may be equal or unequal) intandem, these members giving the delays du, 112 and d13, respectively.The path D3 contains the delay members M, 15 and 16 (which may be equalor unequal) having delays of 131, (132 and (133,168- spectively. Signalsfrom the input terminals l4, l5 are applied through the attenuating pads11, it and "i9, respectively, to the attenuators 89, BI and 82,respectively. The attenuator is connected to the delay member ll bymeans of the conductors 53 and 84 and is connected to the delay member16 by means of the conductors 85 and 88. The attenuator BI is connectedby means of the conductors 8'! and 88 to the input terminals of themembers 12 and I5 while the attenuatcr 52 is connected by means of theconductors S5 and 533 to the input terminals of the member 53 and bymeans of the conductors 9| and 92 to the input terminals of the delaymember 14. The output terminals of the members D2, 13 and. '55 areconnected to the output terminals 15, ll of the transducer 50. Theseoutput terminals in Fig. 5 are connected to produce regularly recurringhumps in the attenuation versus frequency characteristic of the systemwhile the arrangement of Fig. 4 is connected to produce regularlyrecurring humps in the envelope delay versus frequency characteristic ofthe system but it is to be understood that either of the transducers 35and 45 can be readily adapted by proper connections of these outputterminals to produce humps in either of the envelope delay orattenuation characteristics. In the arrangement of Fig. 5, one largedelay member 15 is used instead of the three delay members 55, 5! and 52in the transducer 39 in Fig. 4 but in the arrangement shown in Fig. 5 afinite delay is required in the path D1 which in the arrangement ofFigs. 1, 2 and i can be zero. In the arrangement of Fig. 5, wiggles areproduced having crests far apart using delays so that the delay in thepath D2 minus the delay in the path D1 equals the delay in the member 15minus the delay in the path D2. Similarly, there are produced wiggleshaving crests close together by proportioning the delays so that thedelay in the path D2 minus the delay in the members l2 and I3 equals thedelay in the members '65 and 35 minus the delay in the path D2. Thispositive delay is greater than the positive delay produced in the pathD2 minus that produced in the path D1. There are also produced wiggleshaving crests still closer together by proportioning the delays so thatthat produced in the path D2 minus that produced in the member 13 equalsthe delay produced in the path D3 minus that produced in the path D2.This is a positive delay much greater than that produced in the paths D2minus that produced in the path D1. Since the delay in the path D1equals d11+d12+d13 and the delay in the path D3 equals d33+d3z+ds1, itfollows that 1211 equals (Z32 and (112 equals (231.

Although the present invention has been described in terms of certainillustrative embodi 2,444,oes

59 forms as may fairly-come within the spirit and letter-of -theappended claims.

What is claimed is:

1. Ina signal transmission system, the method of reducing substantiallyregularly recurring humps in a, transmission characteristic of thesystem which varies with tfrequencywhich comprises diverting a portionof the main signal through two branch paths and passing the main signalthrough a third path, the transmission characteristics of the threepaths being such that the phases of any sinusoidal component of theresultant signal in one of the two branch paths and of the samesinusoidal component of the resultant signal in the other of the twobranch paths are respectively +6 and with respect to the phase of thesame sinusoidal component of thesignal in the thirdpath, where a'is anyconvenient. phase difference, and combining the output signals of thethree paths to form a composite signal.

2. In a signal transmission system, the method of reducing substantiallyregularly recurring humps in an envelope delay versus frequencycharacteristic of the system which comprises diverting portion of themain signal through two branch paths and passing the main signalsthrough a third path, the transmission characteristics of the threepaths being such that the phases of any sinusoidal component of theresultant signal in one of the two branch paths and of the samesinusoidal component of the resultant signal in the other of the twobranch paths are respectively +0 and 0 with respect to the phase of thesame sinusoidal component of the signal in the third path, where 0 isany convenient phase difference, and combining the output signals of thethree paths to form a composite signal.

3. In a signal transmission system, the method of reducing substantiallyregularly recurring humps in attenuation versus frequency characteristicof the system which comprises diverting a portion of the main signalthrough two branch paths and passing the main signals through a thirdpath, the transmission characteristics of the three paths being suchthat the phases of any sinusoidal component of the resultant signal inone of the two branch paths and of the same sinusoidal component of theresultant signal in the other of the two branch paths are respectively+0 and +0 with respect to the phase of the same sinusoidal component ofthe signal in the third path, where 0 is any convenient phasedifference, and combining the output signals of the three paths to forma composite signal.

4. The method of claim 1 in further combination with the step ofrepeating this method with the output signal produced thereby bututilizing paths having transmission characteristics so that 0 has adifferent value than before.

5. In combination, a signal path having impedance irregularities whichproduce a multiplicity of small humps in a transmission characteristicof the path which varies with frequency and a transducer connected insaid signal path for reducing certain ones, at least, of said humps,said transducer comprising means for diverting a portion of thetransducer input signal through two branch paths, means for passinganother portion of this input signal through a third path including adelay member, the transmission characteristics of said three paths beingsuch that output signals are produced having for any particularsinusoidal component phases which are respectively +0 and +0 withrespect to the same 10 sinusoidal component of'the signal produced insaid third path, where 0' is any convenient phase difference, and meansfor combining the output signals of said three paths.

6. In combination, a signal path having impedance irregularities whichproduce a multiplicity of smallhumps in the envelope delay versusfrequency characteristic of said path and a transducer connected in saidsignal path for reducing certain ones, at least, of said humps, saidtransducer comprising means for diverting a portion of the transducerinput signal throug'htwo branch paths, means for passing another portionof this input signal through a third path including a delay member, thetransmission characteristics of said thr'eepaths being such that outputsignals areproduced having for anyparticular sinusoidal component phaseswhich are respectively +9 and +0 with respect to the same sinusoidalcomponent of the signal produced in said third path, where 9 is anyconvenient phase difference, and means for combining the output signalsof said three paths according to the formula l+re+ +re where r is themagnitude of the current in each of the two branch paths referred to themagnitude of the output signal in said third path as unity.

7. In combination, a signal path having impedance irregularities whichproduce a multiplicity of small humps in the attenuation versusfrequency characteristic of said path and a transducer connected in saidsignal path for reducing certain ones, at least, of said humps, saidtransducer comprising means for diverting a portion of the transducerinput signal through two branch paths, means for passing another portionof this input signal through a third path including a delay member, thetransmission characteristics of said three paths being such that outputsignals are produced having for any particular sinusoidal componentphases which are respectively +0 and +0 with respect to the samesinusoidal component of the signal produced in said third path, where 0is any convenient phase difference, and means for combining the outputsignals of said three paths according to the formula where r is themagnitude of the current in each of the branch paths referred to themagnitude of the output signal in said third path as unity.

8. In combination, a signal path having impedance irregularities whichproduce a multiplicity of small humps in a transmission characteristicof the path which varies with frequency and a transducer connected insaid signal path for reducing certain ones, at least, of said humps,said transducer comprising means fordiverting a portion of thetransducer input signal through two branch paths, means for passinganother portion of this input signal through a third path including adelay member, the transmission characteristics of said three paths beingsuch that output signals are produced having for any particularsinusoidal component phases which are respectively 6+ and +0 withrespect to the same sinusoidal component of the signal produced in saidthird path, where 9 is any convenient phase difference, means forcombining the output signals of said three paths, each of said threepaths comprising a plurality of delay members in tandem, and means forpassing portions of the signal in said third path, delayed to extentswhich are less than that of the total delay of said path,

tion of this input signal through 'a third path ineluding a delaymember, the transmission characteristics of said three paths being suchthat output signals are produced having for any particular sinusoidalcomponent phases which are respectively +0 and 9 with respect to thesame sinusoidal component of the signal produced in said third path,where a is any convenient phase difierence, means for combining theoutput signals of said three paths, each of said two branch pathscomprising a plurality of delay members in tandem, and means fordiverting portions of said input signal in each case through one or moreof the members in one of said branch paths and, in addition, through oneor more of the members in another of said paths.

KENNETH \V. PFLEGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,644,395 Pohlman' Oct. 4, 19271,681,252 Nyquist Aug. 21, 1928

